The present invention relates to an apparatus for detecting leakage in an evaporated fuel processing system after an internal-combustion engine is stopped.
Various methods have been proposed for detecting leakage in an evaporated fuel processing system that processes evaporated fuel generated in a fuel tank. Japanese Patent No. 2751758 discloses a method for detecting leakage in an evaporated fuel processing system. According to the method, a change in the pressure of the system is compared with a determination value after the system is placed under a negative pressure. It is determined whether there is leakage in the system based on the comparison result. The determination value is set according to the atmospheric pressure.
Leakage detection for the evaporated fuel processing system may be carried out after the internal-combustion engine is stopped. According to the method disclosed in Japanese Patent Application Unexamined Publication No. 11-336626, the evaporated fuel processing system is placed under a negative pressure after the engine is stopped. Leakage in the evaporated fuel processing system is detected based on a change in the pressure of the system.
Since the atmospheric pressure in highlands is lower than in lowlands, the amount of the evaporated fuel generated in highlands is greater than in lowlands. In highlands, the pressure of the evaporated fuel processing system may significantly increase due to the evaporated fuel.
In a conventional method as described above, a determination value used for the leakage detection is constant regardless of whether the vehicle is located in highlands or lowlands. According to the conventional method, an erroneous determination may be made because the amount of evaporated fuel changes according to whether the vehicle is located in highlands or lowlands.
Therefore, there is a need for an apparatus and a method in which leakage detection is accurately performed regardless of whether the vehicle is located in highlands or lowlands.